The Vatican on Sunday beatified more than 500 "martyrs of the faith" who were killed during the Spanish civil war, despite calls for the pope to cancel the event because of the Catholic church's support for General Francisco Franco.

The 1936-1939 conflict resulted in the victory of Franco's nationalist forces and a 40-year dictatorship that only ended with his death in 1975.

The mass beatification was attended by around 25,000 supporters of the church, among them 4,000 relatives of the victims, and took place amid tight security, with fears that the far-right would try to hijack the ceremony.

The Spanish Episcopal Conference, which organised the event, tries to avoid the term "civil war martyrs" because it argues that "these were not combatants, they were not armed. They died solely because they would not renounce their faith".

In perhaps the most controversial moment, Pope Francis made a televised address to the congregation, but failed to address the church's support for Franco. More than 100 support groups for victims of Franco's forces wrote an open letter to the pope last week, calling on him to apologise for the church's role, which they said helped to legitimise "the military uprising and the Franco dictatorship that claimed so many victims".